Bug 23266: Add to cart fires twice on shelf page

Bug 23266: Add to cart fires twice on shelf page

Remove some duplicate functionality between opac-bottom and opac-shelves.

Test plan:
[1] Before this patch, add to cart from a shelf page. Observe that the
    basket count is incremented with 2.
[2] After this patch, it should be incremented with 1.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>